An ordinary network infrastructure includes a plurality of network devices connected together in a wired or wireless way. The wireless way may be an Ad-hoc network mode, a mesh mode, or another mode. In the situation of a wireless network, the network infrastructure includes a plurality of wireless access devices enabling the host devices to access networks wirelessly. The wireless access devices may be also connected with the rear-end routers, transmitting the packets output by the host devices through the routers. In order to administer the network conveniently, the administrator usually divides the network into many subnetworks. The host device will connect with one subnetwork, using the Internet protocol address (IP address) of the subnetwork. While roaming to a new subnetwork, the host device must assume the IP address of the new subnetwork for Internet access.
On the other side, a host device may turn from the original network device to connect with a new network device. If the new network device and the original network device respectively belong to different subnetworks, a series of handover procedures must be undertaken to hand over the host device to the new network device. The aforementioned handover procedures include a Layer-3 handover operation. In the Layer-3 handover operation, the host device maybe request a new IP address from the new network device to update the IP address and maintain the network connectivity.
An IP address had two functions. The first function is to act as the basis of routing. In other words, while a host device moves to a different subnetwork, the IP address of the host device would change so that the packets can be correctly transferred. The second function is to act as the endpoint identifier of the transport layer and the application layer. In the case of transmission control protocol (TCP) session, two sets of network sockets are used as the basis of network connection. A socket is formed by an IP address and a TCP port. Once the IP address or the TCP port of either socket set changes, the TCP session connection would be interrupted.
Therefore, it is a target of the technicians in the field to provide a network system and a related operation method, which have a better handover mechanism, to achieve seamless handover and decrease the time spent in handover procedures.